I have a function That prints after gettign the value form a Ultimate Picker

umbraco.NodeFactory.Node.GetCurrent().GetProperty("backCover").Value

but what if the user does nto choose a media item and saves  the node

i want to make sur eit genrates print application even without the umbraco.NodeFactory.Node.GetCurrent().GetProperty("backCover").Value

such as

if (umbraco.NodeFactory.Node.GetCurrent().GetProperty("backCover").Value == null)
                {
                     document.Close();


                }
                else
                {
                    document.NewPage();
                    umbraco.cms.businesslogic.media.Media nm = new umbraco.cms.businesslogic.media.Media(Int32.Parse(umbraco.NodeFactory.Node.GetCurrent().GetProperty("backCover").Value));

                    string fileNameExisting = Server.MapPath(nm.getProperty("umbracoFile").Value.ToString());


                    PdfReader reader = new PdfReader(fileNameExisting);
                    PdfImportedPage page = writer.GetImportedPage(reader, 1);
                    iTextSharp.text.Image mimage = iTextSharp.text.Image.GetInstance(page);
                    document.Add(mimage);

                   
                }

                document.Close();

i also tried If( umbraco.NodeFactory.Node.GetCurrent().GetProperty("backCover").Value !=null)

but it gives this error Input string not in correct format

any solutions or code samples on how i can sovle this problem